Multi-channel SDMA

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/090,518 filed Aug. 20, 2008, which is herein incorporated by reference in its entirety.

BACKGROUND

In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single base station by sharing the same channel (same time and frequency resources) while achieving high data throughputs. One such scheme is spatial division multiple access (SDMA).

In SDMA systems, a base station may transmit or receive different signals to or from a plurality of mobile user terminals at the same time and using the same frequency. In order to achieve reliable data communication, user terminals may need to be located in sufficiently different directions. Independent signals may be simultaneously transmitted from each of space-separated antennas at the base station. Consequently, the combined transmissions may be directional, i.e., the signal that is dedicated for each user terminal may be relatively strong in the direction of that particular user terminal and sufficiently weak in directions of other user terminals. Similarly, the base station may simultaneously receive on the same frequency the combined signals from multiple user terminals through each of antennas separated in space, and the combined received signals from multiple antennas may be split into independent signals transmitted from each user terminal by applying the appropriate signal processing technique.

A multiple-input multiple-output (MIMO) wireless system employs multiple (N_T) transmit antennas and multiple (N_R) receive antennas for data transmission. A MIMO channel formed by the N_Ttransmit and N_Rreceive antennas may be decomposed into N_Sspatial channels, where N_S≦min {N_T,N_R}. The N_Sspatial channels may be used to transmit N_Sindependent data streams to achieve greater overall throughput.

In a multiple-access MIMO system based on SDMA, an access point can communicate with one or more user terminals at any given moment. If the access point communicates with a single user terminal, then the N_Ttransmit antennas are associated with one transmitting entity (either the access point or the user terminal), and the N_Rreceive antennas are associated with one receiving entity (either the user terminal or the access point). The access point can also communicate with multiple user terminals simultaneously via SDMA. For SDMA, the access point utilizes multiple antennas for data transmission and reception, and each of the user terminals typically utilizes one antenna for data transmission and multiple antennas for data reception.

SUMMARY

Certain embodiments provide a method for scheduling packet transmissions in a multi-channel wireless communications system. The method generally includes receiving an identification of channels available for communicating simultaneously with a plurality of wireless network nodes via a spatial division multiple access (SDMA) scheme, determining a schedule for packet transmission for the wireless network nodes based on the identification of channels, and transmitting downlink packets to at least some of the wireless network nodes simultaneously via the SDMA scheme according to the schedule.

Certain embodiments provide a method for scheduling packet transmissions in a multi-channel wireless communications system. The method generally includes sending an identification of one or more channels available for communicating with the wireless network nodes as an uplink spatial division multiple access (SDMA) transmission and receiving a downlink SDMA transmission on at least one of the identified communications channels.

Certain embodiments provide a method for scheduling packet transmissions in a multi-channel wireless communications system. The method generally includes receiving an identification of channels available for communicating with a plurality of wireless network nodes, determining a schedule for packet transmission for the wireless network nodes based on the identification of channels, and communicating the schedule to the wireless network nodes.

Certain embodiments provide a method for scheduling packet transmissions in a multi-channel wireless communications system. The method generally includes sending an identification of one or more channels available for communicating with the wireless network, receiving a schedule for communicating with the wireless network generated based on the identification of channels, and communicating with the wireless network according to the schedule.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes means for receiving an identification of channels available for communicating simultaneously with a plurality of wireless network nodes via a spatial division multiple access (SDMA) scheme, means for determining a schedule for packet transmission for the wireless network nodes based on the identification of channels, and means for transmitting downlink packets to at least some of the wireless network nodes simultaneously via the SDMA scheme according to the schedule.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes means for sending an identification of one or more channels available for communicating with the wireless network nodes as an uplink spatial division multiple access (SDMA) transmission, and means for receiving a downlink SDMA transmission on at least one of the identified communications channels.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes means for receiving an identification of channels available for communicating with a plurality of wireless network nodes, means for determining a schedule for packet transmission for the wireless network nodes based on the identification of channels, and means for communicating the schedule to the wireless network nodes.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes means for sending an identification of one or more channels available for communicating with the wireless network, means for receiving a schedule for communicating with the wireless network generated based on the identification of channels, and means for communicating with the wireless network according to the schedule.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes a receiver configured to receive an identification of channels available for communicating simultaneously with a plurality of wireless network nodes via a spatial division multiple access (SDMA) scheme, a scheduler configured to determine a schedule for packet transmission for the wireless network nodes based on the identification of channels, and a transmitter configured to transmit downlink packets to at least some of the wireless network nodes simultaneously via the SDMA scheme according to the schedule.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes a transmitter configured to send an identification of one or more channels available for communicating with the wireless network nodes as an uplink spatial division multiple access (SDMA) transmission and a receiver configured to receive a downlink SDMA transmission on at least one of the identified communications channels.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes a receiver configured to receive an identification of channels available for communicating with a plurality of wireless network nodes, a scheduler configured to determine a schedule for packet transmission for the wireless network nodes based on the identification of channels, and logic configured to communicate the schedule to the wireless network nodes.

Certain embodiments provide an apparatus for scheduling packet transmissions in a multi-channel wireless communications system. The apparatus generally includes a transmitter configured to send an identification of one or more channels available for communicating with the wireless network, a receiver configured to receive a schedule for communicating with the wireless network generated based on the identification of channels, and logic configured to communicate with the wireless network according to the schedule.

Certain embodiments provide a computer-program product for scheduling packet transmissions in a multi-channel wireless network comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors. The instructions generally include instructions for receiving, from a plurality of wireless network nodes, an identification of channels available for communicating with the wireless network nodes, determining a schedule for packet transmission for the wireless network nodes based on the identification of channels, and communicating the schedule to the wireless network nodes.

Certain embodiments provide a computer-program product for scheduling packet transmissions in a multi-channel wireless network comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors. The instructions generally include instructions for sending an identification of one or more channels available for communicating with the wireless network, receiving a schedule for communicating with the wireless network generated based on the identification of channels, and communicating with the wireless network according to the schedule.

Certain embodiments provide a computer-program product for scheduling packet transmissions in a multi-channel wireless network comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors. The instructions generally include instructions for receiving an identification of channels available for communicating with a plurality of wireless network nodes, determining a schedule for packet transmission for the wireless network nodes based on the identification of channels, and communicating the schedule to the wireless network nodes.

Certain embodiments provide a computer-program product for scheduling packet transmissions in a multi-channel wireless network comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors. The instructions generally include instructions for sending an identification of one or more channels available for communicating with the wireless network, receiving a schedule for communicating with the wireless network generated based on the identification of channels, and communicating with the wireless network according to the schedule.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective embodiments.

<figref idrefs="DRAWINGS">FIG. 1</figref> shows a spatial division multiple access MIMO wireless system in accordance with certain embodiments of the present disclosure.

<figref idrefs="DRAWINGS">FIG. 2</figref> shows a block diagram of an access point and two user terminals in accordance with certain embodiments of the present disclosure.

<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates example components of a wireless device in accordance with certain embodiments of the present disclosure.

<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates example operations for scheduling transmissions in an SDMA system in accordance with certain embodiments of the present disclosure.

<figref idrefs="DRAWINGS">FIG. 4A</figref> illustrates example components capable of performing the operations shown in <figref idrefs="DRAWINGS">FIG. 4</figref>.

<figref idrefs="DRAWINGS">FIGS. 5 and 6</figref> are example timing diagrams showing example message flows for scheduling transmissions in an SDMA system.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

The multi-antenna transmission techniques described herein may be used in combination with various wireless technologies such as Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiplexing (OFDM), Time Division Multiple Access (TDMA), and so on. Multiple user terminals can concurrently transmit/receive data via different (1) orthogonal code channels for CDMA, (2) time slots for TDMA, or (3) subbands for OFDM. A CDMA system may implement IS-2000, IS-95, IS-856, Wideband-CDMA (W-CDMA), or some other standards. An OFDM system may implement IEEE 802.11 or some other standards. A TDMA system may implement GSM or some other standards. These various standards are known in the art.

<figref idrefs="DRAWINGS">FIG. 1</figref> shows a multiple-access MIMO system <b>100</b> with access points and user terminals. For simplicity, only one access point <b>110</b> is shown in <figref idrefs="DRAWINGS">FIG. 1</figref>. An access point is generally a fixed station that communicates with the user terminals and may also be referred to as a base station or some other terminology. A user terminal may be fixed or mobile and may also be referred to as a mobile station, a wireless device or some other terminology. Access point <b>110</b> may communicate with one or more user terminals <b>120</b> at any given moment on the downlink and uplink. The downlink (i.e., forward link) is the communication link from the access point to the user terminals, and the uplink (i.e., reverse link) is the communication link from the user terminals to the access point. A user terminal may also communicate peer-to-peer with another user terminal. A system controller <b>130</b> couples to and provides coordination and control for the access points.

While portions of the following disclosure will describe user terminals <b>120</b> capable of communicating via SDMA, for certain embodiments, the user terminals <b>120</b> may also include some user terminals that do not support SDMA. Thus, for such embodiments, an AP <b>110</b> may be configured to communicate with both SDMA and non-SDMA user terminals. This approach may conveniently allow older versions of user terminals (“legacy” stations) to remain deployed in an enterprise, extending their useful lifetime, while allowing newer SDMA user terminals to be introduced as deemed appropriate.

System <b>100</b> employs multiple transmit and multiple receive antennas for data transmission on the downlink and uplink. Access point <b>110</b> is equipped with N_apantennas and represents the multiple-input (MI) for downlink transmissions and the multiple-output (MO) for uplink transmissions. A set of N_uselected user terminals <b>120</b> collectively represents the multiple-output for downlink transmissions and the multiple-input for uplink transmissions. For pure SDMA, it is desired to have N_ap≧N_u≧1 if the data symbol streams for the N_uuser terminals are not multiplexed in code, frequency or time by some means. N_umay be greater than N_apif the data symbol streams can be multiplexed using different code channels with CDMA, disjoint sets of subbands with OFDM, and so on. Each selected user terminal transmits user-specific data to and/or receives user-specific data from the access point. In general, each selected user terminal may be equipped with one or multiple antennas (i.e., N_ut≧1). The N_uselected user terminals can have the same or different number of antennas.

SDMA system <b>100</b> may be a time division duplex (TDD) system or a frequency division duplex (FDD) system. For a TDD system, the downlink and uplink share the same frequency band. For an FDD system, the downlink and uplink use different frequency bands. MIMO system <b>100</b> may also utilize a single carrier or multiple carriers for transmission. Each user terminal may be equipped with a single antenna (e.g., in order to keep costs down) or multiple antennas (e.g., where the additional cost can be supported).

<figref idrefs="DRAWINGS">FIG. 2</figref> shows a block diagram of access point <b>110</b> and two user terminals <b>120</b><i>m </i>and <b>120</b><i>x </i>in MIMO system <b>100</b>. Access point <b>110</b> is equipped with N_apantennas <b>224</b><i>a </i>through <b>224</b><i>ap. </i>User terminal <b>120</b><i>m </i>is equipped with N_ut,mantennas <b>252</b><i>ma </i>through <b>252</b><i>mu</i>, and user terminal <b>120</b><i>x </i>is equipped with N_ut,xantennas <b>252</b><i>xa </i>through <b>252</b><i>xu. </i>Access point <b>110</b> is a transmitting entity for the downlink and a receiving entity for the uplink. Each user terminal <b>120</b> is a transmitting entity for the uplink and a receiving entity for the downlink. As used herein, a “transmitting entity” is an independently operated apparatus or device capable of transmitting data via a wireless channel, and a “receiving entity” is an independently operated apparatus or device capable of receiving data via a wireless channel. In the following description, the subscript “dn” denotes the downlink, the subscript “up” denotes the uplink, N_upuser terminals are selected for simultaneous transmission on the uplink, N_dnuser terminals are selected for simultaneous transmission on the downlink, N_apmay or may not be equal to N_dn, and N_upand N_dnmay be static values or can change for each scheduling interval. The beam-steering or some other spatial processing technique may be used at the access point and user terminal.

On the uplink, at each user terminal <b>120</b> selected for uplink transmission, a TX data processor <b>288</b> receives traffic data from a data source <b>286</b> and control data from a controller <b>280</b>. TX data processor <b>288</b> processes (e.g., encodes, interleaves, and modulates) the traffic data {d_up,m} for the user terminal based on the coding and modulation schemes associated with the rate selected for the user terminal and provides a data symbol stream {s_up,m} A TX spatial processor <b>290</b> performs spatial processing on the data symbol stream {s_up,m} and provides N_ut,mtransmit symbol streams for the N_ut,mantennas. Each transmitter unit (TMTR) <b>254</b> receives and processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) a respective transmit symbol stream to generate an uplink signal. N_ut,mtransmitter units <b>254</b> provide N_ut,muplink signals for transmission from N_ut,mantennas <b>252</b> to the access point.

N_upuser terminals may be scheduled for simultaneous transmission on the uplink. Each of these user terminals performs spatial processing on its data symbol stream and transmits its set of transmit symbol streams on the uplink to the access point.

At access point <b>110</b>, N_apantennas <b>224</b><i>a </i>through <b>224</b><i>ap </i>receive the uplink signals from all N_upuser terminals transmitting on the uplink. Each antenna <b>224</b> provides a received signal to a respective receiver unit (RCVR) <b>222</b>. Each receiver unit <b>222</b> performs processing complementary to that performed by transmitter unit <b>254</b> and provides a received symbol stream. An RX spatial processor <b>240</b> performs receiver spatial processing on the N_apreceived symbol streams from N_apreceiver units <b>222</b> and provides N_uprecovered uplink data symbol streams. The receiver spatial processing is performed in accordance with the channel correlation matrix inversion (CCMI), minimum mean square error (MMSE), soft interference cancellation (SIC), or some other technique. Each recovered uplink data symbol stream {s_up,m} is an estimate of a data symbol stream {s_up,m} transmitted by a respective user terminal. An RX data processor <b>242</b> processes (e.g., demodulates, deinterleaves, and decodes) each recovered uplink data symbol stream {s_up,m} in accordance with the rate used for that stream to obtain decoded data. The decoded data for each user terminal may be provided to a data sink <b>244</b> for storage and/or a controller <b>230</b> for further processing.

On the downlink, at access point <b>110</b>, a TX data processor <b>210</b> receives traffic data from a data source <b>208</b> for N_dnuser terminals scheduled for downlink transmission, control data from a controller <b>230</b>, and possibly other data from a scheduler <b>234</b>. The various types of data may be sent on different transport channels. TX data processor <b>210</b> processes (e.g., encodes, interleaves, and modulates) the traffic data for each user terminal based on the rate selected for that user terminal. TX data processor <b>210</b> provides N_dndownlink data symbol streams for the N_dnuser terminals. A TX spatial processor <b>220</b> performs spatial processing on the N_dndownlink data symbol streams, and provides N_aptransmit symbol streams for the N_apantennas. Each transmitter unit <b>222</b> receives and processes a respective transmit symbol stream to generate a downlink signal. N_aptransmitter units <b>222</b> providing N_apdownlink signals for transmission from N_apantennas <b>224</b> to the user terminals.

At each user terminal <b>120</b>, N_ut,mantennas <b>252</b> receive the N_apdownlink signals from access point <b>110</b>. Each receiver unit <b>254</b> processes a received signal from an associated antenna <b>252</b> and provides a received symbol stream. An RX spatial processor <b>260</b> performs receiver spatial processing on N_ut,mreceived symbol streams from N_ut,mreceiver units <b>254</b> and provides a recovered downlink data symbol stream {s_dn,m} for the user terminal. The receiver spatial processing is performed in accordance with the CCMI, MMSE or some other technique. An RX data processor <b>270</b> processes (e.g., demodulates, deinterleaves and decodes) the recovered downlink data symbol stream to obtain decoded data for the user terminal.

At each user terminal <b>120</b>, a channel estimator <b>278</b> estimates the downlink channel response and provides downlink channel estimates, which may include channel gain estimates, SNR estimates, and so on. Similarly, a channel estimator <b>228</b> estimates the uplink channel response and provides uplink channel estimates. Controller <b>280</b> for each user terminal typically derives the spatial filter matrix for the user terminal based on the downlink channel response matrix H_dn,mfor that user terminal. Controller <b>230</b> derives the spatial filter matrix for the access point based on the effective uplink channel response matrix H_up,eff. Controller <b>280</b> for each user terminal may send feedback information (e.g., the downlink and/or uplink steering vectors, SNR estimates, and so on) to the access point. Controllers <b>230</b> and <b>280</b> also control the operation of various processing units at access point <b>110</b> and user terminal <b>120</b>, respectively.

<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates various components that may be utilized in a wireless device <b>302</b> that may be employed within the system <b>100</b>. The wireless device <b>302</b> is an example of a device that may be configured to implement the various methods described herein. The wireless device <b>302</b> may be an access point <b>110</b> or a user terminal <b>120</b>.

The wireless device <b>302</b> may include a processor <b>304</b> which controls operation of the wireless device <b>302</b>. The processor <b>304</b> may also be referred to as a central processing unit (CPU). Memory <b>306</b>, which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor <b>304</b>. A portion of the memory <b>306</b> may also include non-volatile random access memory (NVRAM). The processor <b>304</b> typically performs logic and arithmetic operations based on program instructions stored within the memory <b>306</b>. The instructions in the memory <b>306</b> may be executable to implement the methods described herein.

The wireless device <b>302</b> may also include a housing <b>308</b> that may include a transmitter <b>310</b> and a receiver <b>312</b> to allow transmission and reception of data between the wireless device <b>302</b> and a remote location. The transmitter <b>310</b> and receiver <b>312</b> may be combined into a transceiver <b>314</b>. A plurality of transmit antennas <b>316</b> may be attached to the housing <b>308</b> and electrically coupled to the transceiver <b>314</b>. The wireless device <b>302</b> may also include (not shown) multiple transmitters, multiple receivers, and multiple transceivers.

The wireless device <b>302</b> may also include a signal detector <b>318</b> that may be used in an effort to detect and quantify the level of signals received by the transceiver <b>314</b>. The signal detector <b>318</b> may detect such signals as total energy, energy per subcarrier per symbol, power spectral density and other signals. The wireless device <b>302</b> may also include a digital signal processor (DSP) <b>320</b> for use in processing signals.

The various components of the wireless device <b>302</b> may be coupled together by a bus system <b>322</b>, which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus . . .

As used herein, the term “legacy” generally refers to wireless network nodes that support 802.11n or earlier versions of the 802.11 standard.

While certain techniques are described herein with reference to SDMA, those skilled in the art will recognize the techniques may be generally applied in systems utilizing any type of multiple access schemes, such as SDMA, OFDMA, CDMA, and combinations thereof.

Multichannel SDMA

SDMA may be used for improving utilization of the air link by scheduling multiple terminals for simultaneous transmission and reception using multiple channels. Data may be sent to each of the terminals using spatial streams. Certain embodiments of the present disclosure provide a protocol for efficient scheduling of the spatial streams for multiple terminals over multiple channels.

When considering the unlicensed spectrum available for the 802.11 wireless local area network (WLAN) systems, there is a significant amount of bandwidth available for the packet transmissions. Typically the bandwidth is split into different channels that are 20 MHz wide. If there is more than one single channel free in a distribution system, better utilization of this resource will enable higher aggregate throughputs. Certain embodiments of the present disclosure provide a methodology (protocol) for combining SDMA with the use of multiple channels to enhance the overall aggregate network throughput.

According to certain aspects, the protocol presented in the present disclosure allows an AP to determine a schedule for use in communicating with a plurality of wireless nodes (e.g., stations) over a plurality of wireless channels. In other words, the schedule may identify which, of the plurality of wireless nodes, communicate on which channels. According to certain aspects, the protocol may also provide for training of stations, wherein the AP may utilize sounding signals received from the stations to determine channel information for each station. The AP may use this channel information to optimize subsequent downlink SDMA transmissions to the stations.

<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates example operations for scheduling transmissions in an SDMA system for multiple users over multiple channels in a wireless LAN system, according to certain embodiments of the present disclosure. <figref idrefs="DRAWINGS">FIG. 4</figref> illustrates operations that may performed by both the access points and operations performed by stations. In SDMA systems, the station operations may be performed simultaneously by multiple stations. The illustrated operations may be performed by any suitable components, such as those described above with reference to <figref idrefs="DRAWINGS">FIG. 3</figref>.

For the sake of illustration, the operations of <figref idrefs="DRAWINGS">FIG. 4</figref> are described below in conjunction with example timing diagrams illustrated in <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>. The operations begin, at <b>410</b>, where an access point (AP) sends a request to stations (STAs) for identification of available channels. For example, the request may take the form of a free channel request message (FCRM) <b>502</b> shown in <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>.

At <b>420</b>, the request is received by the STAs. At <b>430</b>, each STA sends an identification of available channels. At <b>440</b>, the identification of available channels sent by each STA is received by the AP. At <b>450</b>, the AP determines a schedule for packet transmissions based, at least in part, on the available channels. At <b>460</b>, the AP communicates the schedule to the STAs. At <b>470</b>, the schedule is received by the STAs. At <b>480</b> and <b>490</b>, the AP and STAs communicate according to the schedule.

For certain embodiments, the AP may not need to send a request in order to receive free channel information from the stations. Thus, operations <b>410</b> and <b>420</b> may be considered optional. For such embodiments, stations may send their free channel information periodically, or in response to some other triggering mechanism, such as when a new available channel is detected.

<figref idrefs="DRAWINGS">FIGS. 5 and 6</figref> illustrate example wireless communications between an AP and a plurality of stations (STA<b>1</b>, STA<b>2</b>, STA<b>3</b>, and STA<b>4</b>) using a plurality of wireless channels (a primary channel CH<b>1</b>, CH<b>2</b>, CH<b>3</b>, and CH<b>4</b>). In the figures, the horizontal axes correspond to the different wireless channels. In order to identify which entity is transmitting a particular message, a label is included in the box representing each message. As an example, the label “AP” in the box <b>502</b> representing the free channel request message (FCRM) indicates the AP transmits the FCRM <b>502</b>, while separate labels for “STA<b>1</b>,” STA<b>2</b>,” “STA<b>3</b>,” and “STA<b>4</b>” in boxes <b>504</b> representing a clear to send frame (CTS) indicate that each of the different stations transmits a CTS frame <b>504</b>.

<figref idrefs="DRAWINGS">FIG. 5</figref> is a timing diagram illustrating an example of scheduling SDMA transmissions for multiple users, in accordance with certain embodiments. In the illustrated example, stations respond with “staggered” clear to send (CTS) frames <b>504</b>, meaning stations send the CTS frames are different times.

The illustrated example assumes the following. The AP can transmit different packets on different channels simultaneously, can transmit packets on non-contiguous channels, and sees all four free channels <b>1</b>, <b>2</b>, <b>3</b>, and <b>4</b>. Station <b>1</b> sees channels <b>1</b>, <b>2</b>, and <b>4</b>, Station <b>2</b> sees channels <b>1</b> and <b>4</b>, Station <b>3</b> sees channels <b>1</b>, <b>3</b>, and <b>4</b>, while Station <b>4</b> sees channel <b>1</b> only. Thus, an optimal schedule may be for the AP to use Channel <b>1</b> for SDMA communication with all stations, Channel <b>2</b> for communication with Station <b>2</b>, Channel <b>3</b> for communication with Station <b>3</b>, and Channel <b>4</b> for SDMA communication with Stations <b>1</b>, <b>2</b> and <b>3</b>.

As shown in the example, the AP sends a Free channel request message (FCRM) <b>502</b>, which may be a multicast message for a specific set of nodes (e.g., with the nodes identified in a MAC header). The FCRM <b>502</b> may also contain information regarding the free channels seen by the AP (e.g., as a free channel list-FCL). The FCRM may also contain information indicating when the nodes are to respond with their respective FCL (e.g., in a Free Channel List Message <b>506</b>).

According the certain aspects, the AP may also send a clear to send (CTS) message <b>504</b> to itself (CTS to self) on all the identified free channels, to secure those channels for the exchange for the necessary amount of time. As illustrated, the FCRM and CTS messages sent by the AP may have a duration field setting that results in NAV settings (for the AP and stations) to protect the channels long enough to receive free channel list and sounding information from all the stations.

In response to the FCRM <b>502</b> sent by the AP, each STA may also send a CTS <b>504</b> to itself on all the free channels that station sees. This mechanism may help ensure that these channels are reserved for a period of time until the AP sends a training request (TRQ <b>408</b>) and all the stations respond with a sounding frame <b>510</b>. If there are nodes which identify the same channel as free, they may perform some type of arbitration, for example, sending the CTS to themselves in a staggered fashion with the order for each station determined by their station ID.

In the illustrated example, since all stations see the primary channel (channel <b>1</b>), the stations each send staggered CTSs <b>504</b> on the primary channel, illustratively in order of station number. Similarly, as Stations <b>1</b>, <b>2</b>, and <b>3</b>, all see Channel <b>4</b>, these stations each send staggered CTSs <b>504</b> on Channel <b>4</b>, as well. Since Station <b>1</b> is the only station to see Channel <b>2</b>, it is the only station to send a CTS <b>504</b> on Channel <b>2</b>. Similarly, as Station <b>3</b> is the only station to see Channel <b>3</b>, it is the only station to send a CTS <b>504</b> on Channel <b>3</b>. As illustrated, in this example, each station may send its CTS <b>504</b> on each channel at the same time specified for staggering.

To help the AP determine a schedule for communication with the stations on the multiple channels, the stations may provide an indication of the channels they see (their “available channels”) in an FCL message <b>506</b> to the AP. As illustrated, for certain embodiments, the FCL message <b>506</b> from each station may be transmitted on the (same) primary channel as an SDMA uplink transmission. Such scheduling of the FCL messages <b>506</b> may be specified by the AP in the FCRM <b>502</b>. For example, the FCRM may contain information indicating whether the stations should send their FCL messages <b>506</b> as an SDMA UL transmission (as shown) or in a staggered fashion.

Upon receiving all the FCL messages <b>506</b> from the STAs, the AP may compute schedules indicating the packet transmission for different responding STAs, based on the “available channels” for each station indicated in the free channel lists. The AP may then send some type of multichannel message on all the free channels to reserve these channels around the AP. Such a message may be chosen to be “legacy compatible,” in terms of network allocation vector (NAV) setting capabilities such that stations that are not SDMA-capable may still adjust their NAV settings accordingly. The NAV of the multicast request message should protect the primary channel until all the block acknowledgements (BAs) <b>516</b> are received. The NAV settings on the secondary channels (CH<b>2</b>-CH<b>4</b>) may also be set to protect those channels for the duration of their respective packet transmissions.

According to certain aspects, the multi-channel request message may take the form of training request messages (TRQs) <b>508</b>. As with the FCRM <b>502</b>, according to certain aspects, the stations may respond the TRQs <b>508</b> with staggered CTSs <b>504</b>.

As shown, the TRQs <b>508</b> may be sent on the free channels that are available to multiple stations. The stations receiving the TRQs <b>508</b> may respond by transmitting sounding signals <b>510</b>. The AP may utilize the sounding signals to determine channel information for each station, which may be used to optimize subsequent SDMA transmissions <b>512</b>. For certain embodiments, the CTS and sounding frames may be kept separate, as illustrated, which may allow the format of these messages to be combatable with legacy stations.

After training, the AP may send data to the stations. As illustrated, the AP may send data simultaneously via SDMA transmissions <b>512</b> to Stations <b>1</b>-<b>4</b> on the primary channel. Since Stations <b>1</b>-<b>3</b> all see Channel <b>4</b>, the AP may send data to these stations via SDMA transmissions <b>512</b> on Channel <b>4</b>. The AP may send data via (non-SDMA) transmissions <b>514</b> to Station <b>1</b> on Channel <b>2</b> and to Station <b>3</b> on Channel <b>3</b>, as these are the only stations that see these respective channels. As illustrated, the stations may acknowledge receipt of the data via block acknowledgements (BAs) <b>516</b>. According to certain aspects, the schedules for the BAs <b>516</b> may be carried in the MAC header (of the SDMA data transmissions <b>512</b>). As illustrated, all the SDMA stations may reply with a BA <b>516</b> as an UL SDMA transmission on the primary channel.

<figref idrefs="DRAWINGS">FIG. 6</figref> is a timing diagram illustrating another example of scheduling SDMA transmissions where it is assumed that symbol time of multiple stations is aligned (e.g., symbols sent from multiple stations arrive at the AP substantially aligned). Other assumptions for <figref idrefs="DRAWINGS">FIG. 6</figref>, regarding channel availability to the AP and per station are the same as in <figref idrefs="DRAWINGS">FIG. 5</figref>.

Again, the AP sends an FCRM <b>502</b>, which may be a multicast message for a specific set of nodes and may also contain information regarding the free channels seen by the AP. Due to the symbol time alignment, however, rather than send staggered CTSs <b>504</b>, as in <figref idrefs="DRAWINGS">FIG. 5</figref>, stations may send CTS messages <b>604</b> simultaneously on the same channel. As illustrated, Stations <b>1</b>-<b>4</b> send simultaneous CTS messages <b>604</b> on the primary channel (Channel <b>1</b>) while Stations <b>1</b>-<b>3</b> send simultaneous CTS messages <b>604</b> on Channel <b>4</b>. While Station <b>1</b> and Station <b>3</b> are the only stations that send CTS messages <b>604</b> on Channel <b>2</b> and Channel <b>3</b>, respectively, they may also do so simultaneously.

As illustrated, simultaneous CTS messages <b>604</b> may again be sent in response to the TRQ messages <b>508</b> sent by the AP after receiving the FCL messages <b>506</b>. Thus, in the symbol aligned case, the overall transaction time may be significantly reduced by eliminating the need for staggered CTS messages.

The various operations of methods described above may be performed by various hardware and/or software component(s), logic, and/or module(s) corresponding to means-plus-function blocks illustrated in the figures. Generally, where there are methods illustrated in figures any suitable means having corresponding counterpart means-plus-function figures, the operation blocks correspond to means-plus-function blocks with similar numbering. For example, operations <b>410</b>-<b>480</b> shown in <figref idrefs="DRAWINGS">FIG. 4</figref> may be performed by means <b>410</b>A-<b>480</b>A shown in <figref idrefs="DRAWINGS">FIG. 4A</figref>.

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.

Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals and the like that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles or any combination thereof.

The various illustrative logic blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable means device (PLD), discrete gate or transistor means, discrete hardware components or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in any form of storage medium that is known in the art. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM and so forth. A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. A storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.

The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

The functions described may be implemented in hardware, software, firmware or any combination thereof. If implemented in software, the functions may be stored as one or more instructions on a computer-readable medium. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

Software or instructions may also be transmitted over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission medium.

Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.